1. Field of the Invention
The present invention relates to gas reaction catalysts, and in particular to catalysts for the recombination of the oxyhydrogen gas created by lead-acid storage batteries into water, the catalyst consisting essentially of a catalyst carrier material and an active metallic catalyst material of the platinum group arranged in or on the carrier material. The invention concerns itself with a method of producing such a catalyst and a device for the application of such catalysts in combination with storage batteries in the place of the normally used battery plug, in accordance with German patent application P 20 08 218.2.
2. Description of the Prior Art
Catalysts which are used for the control or acceleration of the speed of a chemical reaction, without being part of the end product obtained by the reaction, consist normally of a catalyst carrier material which is catalytically indifferent and of the catalyst material itself which is applied to the carrier or otherwise arranged on the carrier surface. Because the catalytic reaction takes place within a very thin surface layer of the catalyst material, and because the catalytic reaction is of a surface-chemical nature, a primary desire in the production of this type of catalyst is to obtain a maximum degree of dispersity of the catalyst material so as to obtain the greatest possible reaction surface. With a given chemical composition of the catalyst material itself, any improvement in the catalytic activity therefore can only be obtained through improved production and assembly methods which reflect themselves in the physical characteristics of the catalyst surface. For this reason, it has already been suggested to utilize pulverulent or granular carrier materials and similar granular catalyst materials and to thoroughly intermingle these materials. It has also been suggested to use porous carrier grains and to soak the latter with the active catalyst material. It is further known from the prior art to obtain the catalyst layer on the surface of pre-formed grains of the carrier material by precipitation.
Based on this general technological background, various attempts have already been made to achieve an effective recombination of the oxygen and hydrogen which is created in lead-acid storage batteries to obtain water which can be returned to the electrolyte of the battery, in order to reduce servicing requirements, and especially, to eliminate the frequent addition of distilled water to the electrolyte. For instance, there are commercially available so-called catalytic battery plugs which contain a catalyst arranged inside a housing which consists of a mixture of granular catalyst carrier material and granular activated catalyst material of the platinum group (German Pat. No. 953,354). This container is inserted in the place of a conventional battery plug into the particular battery opening, thereby exposing the catalyst to the atmosphere in the reaction space of the battery so as to recover water from the oxyhydrogen gas which is created during the operation of the storage battery.
However, the basic problem of the recombination of oxygen and hydrogen has not been satisfactorily solved by these catalytic battery plugs. Considerable difficulties have been encountered in connection with the fact that the catalytic reaction is highly exothermic and very difficult to control. It was found, for example, that conditions of very high specific loads on the catalyst surface may occur through the supply of comparatively large amounts of oxygen and hydrogen which cause a concentrated development of reaction heat within a small space consisting of only a few carrier grains which are in immediate contact with the oxyhydrogen gas. The entire grain accumulation of the catalyst-carrier mixture has a very poor heat conductivity, because of the small areas of contact between the grains. This shortcoming is very detrimental to the effective operation of the catalyst, due to the local overloading of the activated metal and carrier material which reduces the longevity of the catalyst. Applicants have in the past attempted to improve the catalyst-carrier mixture by depositing the catalytically active metal such as palladium, for example, through precipitation on carrier materials such as alumina in granular form. It was found, however, that even such an improved deposition of the catalyst material is subject to the shortcomings of poor heat conductivity and lack of uniformity of temperature distribution in the catalyst body as a whole and that the earlier-mentioned shortcomings could not be completely eliminated.
A further difficulty in connection with the catalytic recombination of oxyhydrogen gas in lead-acid batteries stems from the need to eliminate, or at least reduce the poisoning of the active catalyst material through antimony hydride, acid vapors, and other substances which escape from the cells of lead-acid batteries. This makes it necessary to place additional catalyst material into the flow path of the gases. It has already been suggested to use a deposit of aluminum oxide powder with a layer of lead oxide and arrange it on a battery plug in the flow path of the gases ahead of the oxyhydrogen recombination catalyst material itself (U.S. Pat. No. 3,038,954). In this type of catalyst system, which consists of at least two differently active granular deposits of catalyst material, new problems are encountered in connection with the assembly and location of the various deposits, in order to keep them separated, short of providing separate containers for each catalyst. These difficulties are especially serious, when a compact arrangement of the deposits is necessary, as is the case when the inner catalyst consists of granular material with a layer of palladium, and the outer catalyst is likewise of granular material with a layer of lead oxide.